Estimation of soil-specific microbial degradation of alpha-cypermethrin by compound-specific stable isotope analysis.

In this study, the microbial degradation of alpha-cypermethrin was investigated in 14 different soil samples by compound-specific stable isotope analysis. After 40 and 80 days of microbial degradation, the stable carbon isotope ratios of alpha-cypermethrin shifted from - 32.18 to - 31.87‰ ~ - 31.12 and - 31.45‰ ~ - 29.75‰ in the soils, respectively. The microbial degradation percentages of alpha-cypermethrin were calculated as 15.6~44.3% after 40 days of incubation and 33.3~73.9% after 80 days of incubation. The effects of physicochemical properties of soil samples were then explored on the microbial degradation of alpha-cypermethrin. The results revealed that the microbial degradation percentages were positively correlated with the contents of organic carbon in soils with Pearson correlation coefficients of 0.794 and 0.843 for 40 and 80 days of microbial degradation, respectively, indicating that the microbial degradation of alpha-cypermethrin was faster in the soil with higher content of organic carbon. Accordingly, soil-specific use should be considered in practical agricultural application of alpha-cypermethrin to reduce the residue of the pesticide.